No teacher with any professional pride would argue that we shouldn't try to assess a teacher's competence, and determine who is effective, who isn't, and then increase the level of effectiveness. (One would hope that we would try new learning and training to make teachers more effective before we just toss them onto the curb, but that's another discussion.)
The problem is that we still can't figure out how to measure it. And the Economic Policy Institute, a non-partisan research tank has concluded definitively that the system of tying teacher compensation directly and mechanically to student test scores called "Value-Added Measurement" doesn't work.
Here are the final paragraphs of the Executive Summary of the report (emphasis mine):
The biggest problem is, as any middle school science student will tell you, is that we cannot hold all the factors in student learning--other than teaching--constant. The study doesn't say this, but I can say it from experience, experience which has been borne out by colleagues I've discussed it with. There are two and only two reasons for student under-performance. One is an actual identifiable learning disorder or disability. In most cases, there is a way to work with or work around such a problem, provided is correctly identified. The other reason is problems at home. That phrase encompasses a whole heck of a lot of different things, from problems in the parents' marriage to financial difficulties to bereavements or dislocations--the list goes on and on. But the larger point is--problems at home are things that no teacher can do anything about, idealistic TV shows and movies to the contrary. You can't fix a kid's family, and you have no business trying.
Evaluation by competent supervisors and peers...should form the foundation of teacher evaluation systems, with a supplemental role played by multiple measures of student learning gains that, where appropriate, could include test scores. Some districts have found ways to identify, improve, and as necessary, dismiss teachers using strategies like peer assistance and evaluation that offer intensive mentoring and review panels.
These and other approaches should be the focus of experimentation by states and districts.
Adopting an invalid teacher evaluation system and tying it to rewards and sanctions is likely to lead to inaccurate personnel decisions and to demoralize teachers, causing talented teachers to avoid high-needs students and schools, or to leave the profession entirely, and discouraging potentially effective teachers from entering it.Legislatures should not mandate a test-based approach to teacher evaluation that is unproven and likely to harm not only teachers, but also the children they instruct.
This is not to say that we should give up trying to figure out who the good teachers are and why. (Incidentally, another study I read this week found that they could find no common factor of teaching style among effective teachers. So that means it goes deeper than questions of style.) Certainly, teachers can tell by observation who is teaching and who isn't. And by the way, students can tell, too.
And here's the dirty secret of teacher evaluation that no politician or administrator is going to tell you: when we come up with a good system, it's going to cost more than whatever we're doing now. Then, I suspect, all the angry taxpayers will have less interest in teacher accountability, and perhaps the professionals will be left alone to determine the best methods.